Matthew Green speaks at a Johns Hopkins event about the NSA's covert surveillance operations in the U.S. Green, an assistant research professor at the university's Information Security Institute, made news recently when a blog post he wrote critical of the NSA was ordered removed by the school because an administrator mistakenly believed it linked to classified information.

Matthew Green speaks at a Johns Hopkins event about the NSA's covert surveillance operations in the U.S. Green, an assistant research professor at the university's Information Security Institute, made news recently when a blog post he wrote critical of the NSA was ordered removed by the school because an administrator mistakenly believed it linked to classified information. (Tricia Bishop / Baltimore Sun)

Kevin Rector, The Baltimore Sun

A Johns Hopkins University cryptography professor — who gained media attention when university officials told him to take down a blog post he wrote about National Security Agency documents leaked by Edward Snowden — says he declined an invitation this week to join journalists and others reviewing the classified NSA documents.

"The truth is, I don't really know what to say," said Matthew D. Green, who received the invitation from Guardian journalist Glenn Greenwald via Twitter on Thursday.

"It was a very generous offer," Green said. "I think somebody should be down there and they need more expertise to go through those documents, [but] I'm not sure I want it to be me."

Greenwald, who received the documents from Snowden and has led global reporting on them, invited Green to his home in Rio de Janeiro, Brazil, to "work journalistically" on the documents, specifically as they pertain to the NSA's alleged circumvention of online encryption tools.

The invitation gave a boost to Green's rising prominence in the debate over NSA spying methods. Johns Hopkins administrators this month briefly asked him to remove from university servers a blog post he had written about coverage of the Snowden documents.

Hopkins administrators initially said they feared legal repercussions from Green's post but later concluded that fear was unfounded.

The university's short-lived decision raised the hackles of advocates of free speech, in part because, they said, it stifled Green's academic voice on a subject that has been clouded by the inability or unwillingness of other experts to get involved. Green and others believe some have kept quiet for fear of risking government clearances or research contracts they hold.

The invitation to review the documents came after Green, in a Twitter exchange, urged Greenwald to bring more experts into the fold to study the cryptography implications in the documents.

"I think there's more useful information in those documents than you realize. Please do bring in more experts," Green wrote to Greenwald on the social media outlet.

Greenwald responded quickly: "Any time you'd like to come to Rio to work journalistically on the docs, that'd be great — let me know."

Greenwald and other journalists in his circle have largely — though not entirely — restricted access to the Snowden documents to themselves and partners in media outlets such as the Guardian and The New York Times.

After Greenwald's invitation, Green took a step back, saying in part he didn't "want to end up having to keep secrets" like researcher and cryptographer Bruce Schneier, who has been brought into Greenwald's circle.

On Friday, Green, who has a wife and two children, said he might have been more inclined to join Greenwald in Brazil 10 years ago. But the international intrigue surrounding Greenwald's work, and the possible dangers that come with it, have discouraged him from leaving his family, he said.

He also doesn't want to give up the role he is playing now, that of commenting openly about the NSA news that Greenwald and others are breaking.

"I like being able to talk to reporters. I like being able to write a blog and speculate wildly about, what does this mean? I don't think there are enough people doing that in my field," he said. "I'm afraid that ... every word that I say if I end up seeing these documents would get parsed for their meaning, and I won't be able to say whatever I want."

Green, who describes himself as a "relatively junior researcher" in his field, said he has been shocked that more of his colleagues in the field of cryptography haven't already spoken up, to express shock at the scope of the NSA's efforts to get around encryption used by so many Americans on a regular basis.

"Sometimes I think I should step back and let some of my more senior colleagues have these conversations, and all I hear are crickets," he said.